The present invention relates to a system for estimating locations of respective information communication terminals, and the information communication terminals used in the system, an agent program, and a location estimation method for the system. More specifically, the present invention relates to a system for estimating locations of respective information communication terminals connected to a wireless local area network (LAN), on the basis of a location of a pseudo-access point that is an information communication terminal connected to a wired LAN; the information communication terminals used in the system; an agent program implemented in each of the information communication terminals, and a location estimation method for the system.
As portable information communication terminals such as a mobile phone, a smartphone, a tablet personal computer (PC), and a notebook PC have become used widely, users have come to always carry such information communication terminals with them. A global positioning system (UPS) function is now equipped in such an information communication terminal, and there are provided many services using location information acquired by using the GPS function.
Such services include displaying the location of the user on a map, guiding the user to a destination, and the like.
There is known a technique by which location information of a mobile terminal is acquired based on information on cells of base stations, information acquired from the GPS, and the like, and is registered in a server by using a long-distance wireless network based on wideband code division multiple access (W-CDMA), personal digital cellular (PDC), CDMA2000 or the like. The technique, however, incurs high usage costs, and thus anew technique is desired by which the location information of the information communication terminal can be acquired simply at low cost.
Recently, a wireless local area network (LAN) which is one of short-distance radio communication systems has been widely spread in the market, and thus there has been proposed a technique of acquiring location information of an information communication terminal simply at low cost by using the wireless LAN.
In addition, a technique has been proposed in which positioning access points are provided, and the detection accuracy of location information is enhanced by using the intensity of the wireless LAN. This technique achieves low cost and enhanced detection accuracy by making radio wave areas small in a way that wireless LAN access points serving as infrastructures for identifying a location are installed in an indoor place where the GPS cannot be used, and are operated to transmit only beacons only necessary for the positioning.
Further, other techniques have been proposed. Specifically, in an ad-hoc mode, a mobile node receives as a beacon packet a packet including location information transmitted from a known terminal through an ad-hoc network, and estimates its own location based on a hop count or the like in the path to the mobile terminal. In the techniques, a terminal acquiring an absolute location by using the GPS advertises its own location information to neighboring terminals, and a terminal receiving the advertised information estimates its own location range based on the advertised information and a hop count in the path from the GPS to the terminal itself.
Meanwhile, one of known techniques of estimating a location based on a radio wave is a received signal strength indication (RSSI) scheme. This scheme uses a relationship between a distance and attenuation of the radio wave intensity, and estimates a distance between a node (end point) supposed to estimate its own location and a node transmitting the radio wave on the basis of the intensity of the received radio wave. The technique will be described by referring to FIG.
FIG. 1 shows that a notebook PC 1 which is an end point is located in coordinates (xEst, yEst, zEst) showing a three-dimensional location. In addition, four notebook PCs 2, 3, 4, and 5 which neighbor the notebook PC 1 and transmit radio waves are respectively located in coordinates (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), and (x4, y4, z4), and respectively have distances r1, r2, r3, and r4 from the notebook PC 1.
Suppose that the notebook PC 1 actually measures the intensities of the radio waves from the notebook PCs 2, 3, 4, and 5 and acquires values p1, p2, p3, and p4. FIG. 2 shows a relationship among the values p1, p2, p3, and p4 and the distances r1, r2, r3, and r4, FIG. 2 shows that the radio wave intensity is inversely proportional to the distance.
In this scheme, distances between the end point and the multiple nodes are estimated, and the three-dimensional coordinates (xEst, yEst, zEst) can be calculated by using the distances in accordance with the following simultaneous equations.(xEst−x1)2⇄(yEst−y1)2+(zEst−z1)2−r12 (xEst−x2)2+(yEst−y2)2+(zEst−z2)2=r22 (xEst−x3)3+(yEst−y3)2+(zEst−z3)2=r32 (xEst−x4)4+(yEst−y4)2+(zEst−z4)2=r42  Formula 1:
There is another technique called a time difference of arrival (TDoA) scheme. This scheme measures a time difference between a radio wave transmission time of a node transmitting a radio wave and a radio wave reception time of an end point and calculates a distance between the node and the end point based on the time difference and the transmission speed of the radio wave.
In a configuration shown in FIG. 1, time differences t1, t2, t3, and t4 are obtained based on times of transmitting radio waves by the notebook PCs 2, 3, 4, and 5 and times of receiving the radio waves by the notebook PC 1. FIG. 3 shows a relationship among the time differences t1, t2, t3, and t4 and the distances r1, r2, r3, and r4, FIG. 3 shows that the time difference is proportional to the distance.
Also in this scheme, distances between the end point and the multiple nodes are estimated. The three-dimensional coordinates (xEst, yEst, zEst) can be calculated by using the distances in accordance with simultaneous equations similar to the Formula 1 above.